Aspen is a pioneer species, moving into open areas quite readily. As the photos below indicate, Aspens love heavy sunlight and they develop there in pure stands. Gradually, however, conifers (which enjoy generating in shade), grow, shade out young Aspens, and produce pure conifer forests. (Click to see photographs showing this succession.)

Aspens spread from dense
systems of underground roots and thus large stands of Aspens are genetically
identical. That is why entire patches of Aspens have similar characteristics:
they retain their
leaves much longer than other Aspens, or they change color earlier than others,
or they turn a particular shade of golden yellow or orange, etc.

Aspen roots continue to live for millennia and even if conifers replace the pioneer Aspens, when the conifers are destroyed by fire, insects, or avalanche the roots become active and generate a new Aspen forest.

Aspens also develop from seeds and can spread this way into areas where they did not exist before.

The surface of Aspen trunks varies from
brilliant white to gray/green and a good deal of this color variation is due to a light, white, chalky powder (see photographs below). Most other species of trees surround themselves with a corky, almost woody bark that grows thicker as the tree grows older, but Aspens shed their outer cells instead of having these develop into a thick bark. The dead cells persist on the thin Aspen bark as a white powder which, under a microscope, looks like a form of snow known as grapple (graupel).

Thickened bark does develop around branch scars, wounds from Elk chew, and other injuries to the thin bark. Also, older trees (at least 30 years of age) develop typical thick tree bark, but even then the thickened bark is only at the base of the tree. Thickened Aspen tree bark does not have the chalky white powder (see photographs below).

Look closely at Aspens and you will see that the thin bark has a green tinge to it. Research has shown that the green pigment in Aspen bark is chlorophyll and that the thin bark photosynthesizes. Aspen bark actually carries on more photosynthesis than Aspen leaves in early spring but leaves win out later in the summer. ("Photosynthesis in Aspen Bark", American Journal of Botany")

Aspens are
afflicted with a number of rots and fungi and it is common to see large
black blotches on their stems. Shallow roots in shallow soils often lead
to tumbling aspens. Stem buds are commonly killed by munching elk or
severe freezes and these afflictions produce bows in the trunks. Snow also bends young Aspens and leaves them with permanent kinks in their trunks. Elk tooth marks, bear claw
marks, and human graffiti are other common deformations Aspens must
endure.

"Populus" is a classical Latin tree name and Linnaeus revived the name for this genus in 1753.
The Greek ending "oides" indicates "resemblance". "Tremuloides" thus means, "resembling the species Populus tremula". "Trem" is Latin for "trembling", used to describe the
manner in which the leaves of both these species (because of their flattened petioles) quiver in the slightest
breeze.

Aspens are the most
widely distributed tree in North America, ranging from
Newfoundland to Alaska, through the Sierras and Rockies to Mexico, and from the
Pacific states across the northern and central tier of states in the United
States to the Atlantic.

The even-aged Aspen
stand in the photograph at left probably sprouted from roots of trees logged
30-50 years
ago. Notice the
tightly packed growth pattern, the lack of lower limbs, and the dark spots on the trunks where old limbs grew. Lower limbs almost always do die (leaving a black
inverted V-shaped scar) and the tree matures to a long, straight, single trunk,
topped by a symmetrical crown of leaves. Trees can grow to three feet in
diameter and 75 feet tall with the lower bark becoming gray and broadly
cracked. Aspens live only about 100 years.

Thin Aspen bark is coated with a fine white powder, sloughed-off dried cells. On the trunk behind Robert Lang's finger tip, you can see the more gray-green bark that showed through after Robert wiped his finger down the trunk.

The outer cells of most trees form a thick bark; Aspen outer cells die, leaving a white powder behind. As Aspens age or when they are injured in some way, the outer cells do form a thick bark.

When you walk Aspen
forests in the spring, use a hand lens and dive into the
miniature beauty of the flowers. Aspens, and other members
of the Willow Family (Salicaceae), are dioecious, that is, they have male flowers
(shown here) on one tree and female flowers on another. In the
photograph at left, hundreds of minute flowers are clustered in each
catkin (a long spike chain). Bracts are brown, finger-like, and
surround creamy yellow flowers (the light creamy color in the photograph
at left) with black-tipped stamens projecting.

Species present and not rareSpecies present and rareSpecies extirpated (historic)Species extinctSpecies noxiousSpecies exotic and presentNative species, but adventive in stateEradicatedQuestionable presence